PROJECT SUMMARY The Zn finger protein MucR is a global regulator of gene expression in the ?-proteobacteria, and a major virulence determinant in Brucella. Despite this importance, surprisingly little is known about how MucR functions at the molecular level beyond the fact that its works predominantly as a transcriptional repressor. We have recently obtained evidence suggesting that MucR serves as an H-NS-like gene silencer in Brucella. This proposed function is consistent with the role that MucR homologs play in other ?-proteobacteria, where they work in concert with antagonistic transcriptional activators to coordinate the proper temporal expression of virulence and symbiosis genes. But demonstrating that the Brucella MucR is an authentic H-NS-like gene silencer would represent a newly described function for a bacterial Zn finger protein. The studies proposed in this application will ? a) utilize chromatin immunoprecipitation massively parallel DNA sequencing (ChIP-seq) and RNA sequencing (RNA-seq) to identify the direct targets of MucR repression in B. abortus 2308; b) employ genetic and biochemical strategies to test the hypothesis that MucR functions as an H-NS-like gene silencer; and c) use cellular and mouse models to test the hypothesis that MucR silencing of specific genes is required for wild-type virulence. If these hypotheses are supported, the proposed studies will define a novel class of bacterial gene silencers, greatly improve our understanding of how Zn finger proteins function in prokaryotic biology, and provide an explanation for why MucR is such an important virulence determinant in Brucella. Successful completion of the proposed studies should also yield information useful for developing improved strategies for preventing and treating human brucellosis, a zoonosis of world-wide importance. There are currently no vaccines that can be safely and effectively used to prevent this disease, and treatment requires prolonged administration of two antibiotics. The extreme and stable attenuation displayed by Brucella mucR mutants makes them attractive as novel vaccine candidates, and the fact that MucR is structurally distinct from eukaryotic Zn finger proteins makes it a viable drug target.